The macrophage is a multipotential cell which contributes to immune defense against tumors by directly killing tumor cells and by releasing immunomodulatory cytokines, including tumor necrosis factor (TNF) and interleukin 1 (IL-1). Macrophages express cytotoxicity which is selective for tumor cells, leaving nontransformed cells unharmed. The mechanisms responsible for the selectivity of macrophage mediated cytotoxicity are not known. The hypothesis to be tested in this project is that macrophages recognize specific tumor cell markers, which activate directed expression o cytotoxic effectors. We have previously shown that tumor cell membranes stimulate macrophages to rapidly release TNF. This cytokine is directly cytocidal for some tumors and exerts broad, immunomodulatory actions which can indirectly contribute to tumor immune defense and host response to neoplastic disease. Because completion of macrophage mediated tumor killing requires up to three days, the principal investigator has chosen to study the directed release of the TNF. The principal investigator has demonstrated that extractable factors from tumor cell membranes specifically stimulate macrophages to release TNF. The aims of the proposed research are to: (1) purify and characterize the tumor associated macrophage activators (TAMA) which stimulate macrophage TNF release; (2) produce monoclonal antibodies against TAMA's (3) determine if TAMA's are also involved in macrophage-mediated high avidity tumor binding; (4) functionally characterize the macrophage surface receptors for TAMA's using radioligand binding assay; and (5) determine if TAMA also stimulate macrophage chemotaxis and IL-1 release. TAMA will be extracted from tumor cell lines using chaotropic agents, semi-purified using biochemical techniques, and tested for activity by stimulating release of TNF from murine peritoneal macrophages. These factors will then be used to immunize rats and ELISA- and functionally screen anti-TAMA monoclonal antibodies. TAMA receptors will then be measured using 125I-labeled, antibody-affinity purified TAMA in radioligand binding assays.